AUTO-EXPOSURE METHOD USING CONTINUOUS VIDEO FRAMES UNDER CONTROLLED ILLUMINATION

• US 20120199654A1
• Filed: 02/03/2011
• Published: 08/09/2012
• Est. Priority Date: 02/03/2011
• Status: Active Grant

• Current Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Original Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Inventors: Zhu, Xiaoxun, Wang, Ynjiun Paul
• Granted Patent: US 8,408,464 B2
• Time in Patent Office: Days
• US Class Current: 235/455
• CPC Class Codes: F21V 33/0052 Audio or video equipment, e.g. televisions, telephones, cameras or computers; Remote control devices therefor
• CPC Class Codes: F21W 2131/30 Lighting for domestic or personal use
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: G06K 7/10732 Light sources
• CPC Class Codes: G06K 7/10752 Exposure time control
• CPC Class Codes: H04N 23/56 provided with illuminating means
• CPC Class Codes: H04N 23/73 by influencing the exposure time

Abstract

An adaptive strobe illumination control process for use in a digital image capture and processing system. In general, the process involves: (i) illuminating an object in the field of view (FOV) with several different pulses of strobe (i.e. stroboscopic) illumination over a pair of consecutive video image frames; (ii) detecting digital images of the illuminated object over these consecutive image frames; and (iii) decode processing the digital images in an effort to read a code symbol graphically encoded therein. In a first illustrative embodiment, upon failure to read a code symbol graphically encoded in one of the first and second images, these digital images are analyzed in real-time, and based on the results of this real-time image analysis, the exposure time (i.e. photonic integration time interval) is automatically adjusted during subsequent image frames (i.e. image acquisition cycles) according to the principles of the present disclosure. In a second illustrative embodiment, upon failure to read a code symbol graphically encoded in one of the first and second images, these digital images are analyzed in real-time, and based on the results of this real-time image analysis, the energy level of the strobe illumination is automatically adjusted during subsequent image frames (i.e. image acquisition cycles) according to the principles of the present disclosure.

Claims

1. A digital image capture and processing system comprising:

a housing having a light transmission aperture;

an image formation and detection subsystem, disposed in said housing, and having image formation optics for projecting a field of view (FOV) through said light transmission aperture and upon an object to be imaged and an image detection array for detecting imaged light reflected off the object during illumination operations in an video image capture mode in which at least a plurality of rows of pixels on said image detection array are enabled;

an illumination subsystem, disposed housing, and employing an array of light sources for producing and projecting a field of narrow-band strobe illumination through a narrow-band transmission-type optical filter realized within said housing, so that said narrow-based strobe illumination is reflected from the illuminated object and transmitted through said narrow-band transmission-type optical filter and detected by said image detection array during said video image capture mode, while all other components of ambient light are substantially rejected;

an automatic illumination control subsystem, disposed in said housing, for controlling the illumination operation of said illumination subsystem so as to carry out an adaptive strobe illumination control process in an automated manner;

an image capturing and buffering subsystem for capturing and buffering 2-D images detected by said image formation and detection subsystem;

a digital image processing subsystem, disposed in said housing, for processing images captured and buffered by the image capturing and buffering subsystem and reading code symbols represented therein and producing symbol character data representative of said read code symbols; and

an input/output subsystem, disposed in said housing, for outputting said symbol character data a host system;

wherein said adaptive strobe illumination control process involves;

(i) said illumination subsystem illuminating said object in said FOV with several different pulses of strobe illumination, over at least a pair of consecutive image frames during said video image capture mode;

(ii) said image formation and detection subsystem detecting digital images of the illuminated object over these consecutive image frames; and

(iii) said digital image processing subsystem decode processing the digital images in effort to read one or more code symbols graphically encoded therein.

2. The digital image capture and processing system of claim 1, wherein said automatic illumination control subsystem, further includes provisions for controlling said exposure duration (i.e. photonic integration time interval) of said image formation and detection subsystem so as to carry out an adaptive strobe illumination and exposure control process in an automated manner;

and wherein (iv) upon failure to read one or more code symbols in one or more of said digital images, analyzing said digital images in real-time, and based on the results of said real-time image analysis, automatically adjusting the exposure duration, and repeating said substeps (i), (ii) and (iii) during subsequent digital image frames.

3. The digital image capture and processing system of claim 1, wherein said illumination subsystem is a LED-based illumination subsystem employing an array of LEDs.

4. The digital image capture and processing system of claim 1, wherein said image detection array is an area-type image detection array.

5. The digital image capture and processing system of claim 4, wherein said area-type image detection array is a CMOS-type area-type image detection array.

6. The digital image capture and processing system of claim 1, wherein said narrow-band transmission-type optical filter is realized within said housing a red-wavelength high-pass reflecting window filter element disposed at said light transmission aperture thereof and a low-pass filter before said image detection array.

7. The digital image capture and processing system of claim 1, wherein said code symbol is a code symbol selected from the group consisting of 1D bar code symbologies, 2D bar code symbologies, and data matrix symbologies.

8. A method of adaptively controlling strobe illumination processes within a digital image capture and processing system supporting an improved level of image acquisition responsiveness, said method comprising the steps of:

(a) providing a digital image capture and processing system including a housing having a light transmission aperture, and containing an image formation and detection subsystem with an image detection array with a video image capture mode, an illumination subsystem with an illumination array, an automatic illumination control subsystem, an image capturing and buffering subsystem, a digital image processing subsystem, and an input/output subsystem interfaced to a host system;

(b) upon detecting an object in the field of view (FOV) of said image formation and detection subsystem, said illumination subsystem illuminates the object in the FOV at a first strobe illumination energy level, while said image detection array is detecting a first digital image of the illuminated object using a predetermined exposure duration, and then said image capture and buffering subsystem capturing and buffering said first digital image;

(c) said digital image processing subsystem attempting to read one or more code symbols graphically represented in the first digital image, and if successful, then generating symbol character data which is sent to said host system, and returning to step (b); and

if decode processing is not successful, then advancing to step (d);

(d) upon detecting an object in the FOV of said image formation and detection subsystem, said illumination subsystem illuminates the object in said FOV at a second strobe illumination energy level, substantially greater than said first strobe illumination energy level, while said image detection array is detecting a second digital image of the illuminated object using the same predetermined exposure duration, and then said image capture and buffering subsystem capturing and buffering said second digital image; and

(e) said digital image processing subsystem attempting to read one or more code symbols graphically represented in said second digital image, and if successful, then generating symbol character data which is sent to said host system, and returning to step (b), and if decode processing is not successful, then advancing to step (f).

9. The method of claim 8, wherein

(f) said digital image processing subsystem analyzing both said first and second digital images, and determining a modified exposure time duration, for subsequent video frames, based upon whether both said first and second digital images as analyzed measures too dark, too bright, or one digital image measures too bright while the other digital image measures too dark;

(g) said illumination subsystem illuminating the object in said FOV at the first strobe illumination energy level, while said image detection array is detecting a first subsequent digital image of the illuminated object using said modified predetermined exposure duration, and then said image capture and buffering subsystem capturing and buffering said first subsequent digital image; and

(h) said digital image processing subsystem attempting to read one or more code symbols graphically represented in said first subsequent digital image, and if successful, then generating symbol character data which is sent to said host system, and returning to step (b).

10. The method of claim 8, which further comprises:

(i) if decode processing is not successful in step (h), then said illumination subsystem illuminating the object in the FOV at said second strobe illumination energy level, substantially greater than said first strobe illumination energy level, while said image detection array is detecting a second subsequent digital image of the illuminated object using the modified predetermined exposure duration, and then said image capture and buffering subsystem capturing and buffering the second subsequent digital image; and

(j) said digital image processing subsystem attempting to read one or more code symbols graphically represented in the second subsequent digital image, and if successful, then generates symbol character data which is sent to said host system, and returning to step (b).

11. The method of claim 10, which further comprises:

(k) if decode processing is not successful in step (j), then returning to step (b).

12. The method of claim 8, wherein said code symbol is a code symbol selected from the group consisting of 1D bar code symbologies, 2D bar code symbologies, and data matrix symbologies.

13. The method of claim 8, wherein said image detection array is an area-type image detection array.

14. The method of claim 13, wherein said area-type image detection array is a CMOS-type area-type image detection array.

15. A method of adaptively controlling strobe illumination processes within a digital image capture and processing system supporting an improved level of image acquisition responsiveness, said method comprising the steps of:

(a) providing a digital image capture and processing system including a housing having a light transmission aperture, and containing an image formation and detection subsystem with an image detection array with a video image capture mode, an illumination subsystem with an illumination array, an automatic illumination and exposure control subsystem, an image capturing and buffering subsystem, a digital image processing subsystem, and an input/output subsystem interfaced to a host system;

(b) upon detecting an object in the field of view (FOV) of said image formation and detection subsystem, said illumination subsystem illuminating the object in the FOV at a first strobe illumination energy level, while said image detection array is detecting a first digital image of the illuminated object using a predetermined exposure duration, and then said image capture and buffering subsystem capturing and buffering said first digital image;

(c) said digital image processing subsystem attempting to read one or more code symbols graphically represented in the first digital image, and if successful, then generating symbol character data which is sent to said host system, and returning to step (b); and

if decode processing is not successful, then advancing to step (d);

(d) upon detecting an object in the FOV of said image formation and detection subsystem, said illumination subsystem illuminates the object in said FOV at a second strobe illumination energy level, substantially greater than said first strobe illumination energy level, while said image detection array detects a second digital image of the illuminated object using the same predetermined exposure duration, and then said image capturing and buffering subsystem captures and buffers said second digital image; and

(e) said digital image processing subsystem attempting to read one or more code symbols graphically represented in said second digital image, and if successful, then generating symbol character data which is sent to said host system, and returning to step (b), and if decode processing is not successful, then advancing to step (f).

16. The method of claim 15, which further comprises:

(f) said digital image processing subsystem analyzing said first and second digital images, and determining a modified exposure time duration, for subsequent video frames, based upon whether said first and second digital images as analyzed measures too dark, too bright, or one digital image measures too bright while the other digital image measures too dark;

(g) said illumination subsystem illuminating the object in the FOV at a first modified strobe illumination energy level, while said image detection array detects a first subsequent digital image of the illuminated object using the same predetermined exposure duration, and then said image capture and buffering subsystem capturing and buffering said first subsequent digital image; and

(h) said digital image processing subsystem attempting to read one or more code symbols graphically represented in said first subsequent digital image, and if successful, then generating symbol character data which is sent to said host system, and returning to step (b).

17. The method of claim 16, which further comprises:

(i) if decode processing is not successful in step (h), then said illumination subsystem illuminates the object in the FOV at a second modified strobe illumination energy level, while said image detection array detects a second subsequent digital image of the illuminated object using the same predetermined exposure duration, and then said image capture and buffering subsystem captures and buffers said second subsequent digital image; and

(j) said digital image processing subsystem attempting to read one or more code symbols graphically represented in said second subsequent digital image, and if successful, then generating symbol character data which is sent to said host system, and returning to step (b).

18. The method of claim 17, which further comprises:

(k) if decode processing is not successful in step (j), then returning to step (b).

19. The method of claim 15, wherein said code symbol is a code symbol selected from the group consisting of 1D bar code symbologies, 2D bar code symbologies, and data matrix symbologies.

20. The method of claim 15, wherein said image detection array is an area-type image detection array.

21. The method of claim 20, wherein said area-type image detection array is a CMOS-type area-type image detection array.